Pancreatic ductal adenocarcinoma (PDA) metastases are poorly understood, limiting the effectiveness of current treatments. An improved understanding of the mechanisms by which PDA metastasizes is critical for the development of effective treatments specific for this disease. We recently identified a PDA-associated antigen, annexin A2 (ANXA2), and demonstrated that tyrosine 23-phosphorylation-dependent cell-surface translocation of ANXA2 is critical for TGFbeta-Rho mediated epithelia-to-mesenchymal transition, invasion and metastasis of PDAs. This proposal aims to delineate the upstream and downstream pathways of ANXA2 to achieve our ultimate goal of identifying new therapeutic targets for PDA treatment. In particular, we hypothesize that two paracrine stromal-to-epithelial axes - the Hedgehog-Insulin-like growth factor I receptor pathway and the hepatocyte growth factor/c-met signaling - form a functional link between PDA stroma and epithelial compartments, resulting in ANXA2 phosphorylation. To understand the effector pathways whereby PDA metastases are promoted following the activation of ANXA2 by phosphorylation, our preliminary studies have led to the second part of our hypothesis that ANXA2 regulates PDA invasion and metastasis through Sema3d/Plxnd1, both belonging to an axon guidance pathway. We therefore propose two aims to test these hypotheses. Specific Aim 1 will elucidate the network of signals that originate in the stroma and result in ANXA2 translocation to the surface of PDA cells. Specific Aim 2 will delineate the downstream effectors of ANXA2 within PDA tumor cells that mediate metastatic spread through axon guidance molecules. The end result will be the elucidation of the complex network of signals that results in cross-talk between the PDA and its microenvironment, and that are mediated through ANXA2 to control PDA invasion and metastasis formation. This in turn, will provide new targets against which to develop novel interventions that disrupt the communication, and in doing so, abrogate tumor progression and metastases.